U.S. patent application number 11/304069 was filed with the patent office on 2006-07-06 for internal combustion engine having an exhaust particulate filter.
This patent application is currently assigned to Nissan Motor Co., Ltd.. Invention is credited to Manabu Miura.
Application Number | 20060144038 11/304069 |
Document ID | / |
Family ID | 36118310 |
Filed Date | 2006-07-06 |
United States Patent
Application |
20060144038 |
Kind Code |
A1 |
Miura; Manabu |
July 6, 2006 |
Internal combustion engine having an exhaust particulate filter
Abstract
A control unit prevents overheating of a particulate filter in
an exhaust path of an internal combustion engine during
regeneration of the particulate filter if the regeneration deviates
from prescribed conditions. Overheating is prevented using one of
two engine operations: a first operation with a relatively lower
exhaust temperature and relatively higher oxygen surplus (lean
operation), or a second operation with a relatively higher exhaust
temperature and a relatively lower oxygen surplus (rich operation).
Based on the filter temperature and amount of particulate sediment,
a heating value in the particulate filter (the heat quantity of an
oxidation reaction of burning particulates in the particulate
filter) is calculated for each operation. The heat released from
the particulate filter to exhaust is also calculated for each
operation. The operation with a lower heat budget, i.e., the
difference between the heating value and heat released is selected
to cool the filter.
Inventors: |
Miura; Manabu; (Zushi-shi,
JP) |
Correspondence
Address: |
SHUMAKER & SIEFFERT, P. A.
8425 SEASONS PARKWAY
SUITE 105
ST. PAUL
MN
55125
US
|
Assignee: |
Nissan Motor Co., Ltd.
Yokohama-shi
JP
|
Family ID: |
36118310 |
Appl. No.: |
11/304069 |
Filed: |
December 15, 2005 |
Current U.S.
Class: |
60/286 ; 60/285;
60/295; 60/297 |
Current CPC
Class: |
F02D 41/029 20130101;
Y02T 10/12 20130101; F02D 2041/0022 20130101; Y02T 10/20 20130101;
Y02T 10/40 20130101; Y02T 10/42 20130101; F01N 3/021 20130101 |
Class at
Publication: |
060/286 ;
060/295; 060/297; 060/285 |
International
Class: |
F01N 3/00 20060101
F01N003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 16, 2004 |
JP |
2004-364479 |
Claims
1. An internal combustion engine comprising: a filter in an exhaust
path of the internal combustion engine that captures particulates
from exhaust in the exhaust path; an inlet air throttle in an
intake air path of the internal combustion engine that control
intake air amount; a fuel injection that spray fuel to supply to
the internal combustion engine; and a control unit that determines
a regeneration condition when an amount of particulate sediment is
greater than a predetermined value, controls the intake air amount
and a fuel injection amount with control signals when the
regeneration condition is determined, determines when regeneration
conditions deviate from prescribed regeneration conditions during
regeneration of the filter and selects one of: a first engine
operation that increases heat transfer from the filter to the
exhaust, and a second engine operation that limits particulate
combustion in the filter.
2. The internal combustion engine of claim 1, wherein the first
engine operation provides a first exhaust temperature and a first
oxygen surplus, and the second engine operation provides a second
exhaust temperature and a second oxygen surplus, and wherein the
first exhaust temperature is lower than the second exhaust
temperature, and the first oxygen surplus is higher than the second
oxygen surplus.
3. The internal combustion engine of claim 1, wherein the control
unit selects one of the first engine operation and the second
engine operation as a function of a temperature of the filter and
an amount of particulate sediment in the filter.
4. The internal combustion engine of claim 1, wherein the control
unit selects one of the first engine operation and the second
engine operation as a function of a first heat budget corresponding
to the first engine operation and a second heat budget
corresponding to the second engine operation, wherein the first
heat budget includes a first heat quantity from a first oxidation
reaction of burning accumulated particulates in the filter and a
first quantity of negative heat transfer between the filter and the
exhaust, and wherein the second heat budget includes a second heat
quantity from a second oxidation reaction of burning accumulated
particulates in the filter and a second quantity of negative heat
transfer between the filter and the exhaust.
5. The internal combustion engine of claim 4, wherein the control
unit selects one of the first engine operation and the second
engine operation by comparing the first heat budget and the second
heat budget and selecting the operation with the lowest
corresponding heat budget.
6. The internal combustion engine of claim 4, wherein the control
unit calculates the first heat quantity using a temperature of the
filter, an amount of particulate sediment in the filter, and an
oxygen concentration in the exhaust entering the filter as
inputs.
7. The internal combustion engine of claim 6, wherein the control
unit calculates the temperature of the filter using inputs from a
first exhaust temperature sensor at an inlet side of the filter and
a second exhaust temperature sensor at an outlet side of the
filter.
8. The internal combustion engine of claim 6, wherein the control
unit calculates the amount of particulate sediment in the filter
using a differential pressure of the filter, and a flow rate of the
exhaust as inputs.
9. The internal combustion engine of claim 6, wherein the control
unit calculates the oxygen concentration according to operation of
the internal combustion engine under the first engine
operation.
10. The internal combustion engine of claim 4, wherein the control
unit calculates the first quantity of negative heat transfer using
a temperature of the filter, an exhaust temperature entering the
filter, and a flow rate of the exhaust as inputs.
11. The internal combustion engine of claim 10, wherein the control
unit calculates the exhaust temperature according to operation of
the internal combustion engine under the first engine
operation.
12. The internal combustion engine of claim 10, wherein the control
unit calculates the flow rate using air flow measured by an air
flow meter in an engine inlet system, and an injection quantity
measured at a fuel injection valve.
13. A method comprising: determining whether regeneration
conditions deviate from prescribed regeneration conditions during
regeneration of an exhaust particulate filter; and in response to
the determination, selecting one of: a first engine operation that
increases heat transfer from the filter to exhaust passing through
the filter, and a second engine operation that limits particulate
combustion in the filter.
14. The method of claim 13, wherein the first engine operation
provides a first exhaust temperature and a first oxygen surplus,
and the second engine operation provides a second exhaust
temperature and a second oxygen surplus, wherein the first exhaust
temperature is lower than the second exhaust temperature, and the
first oxygen surplus is higher than the second oxygen surplus.
15. The method of claim 13, further comprising: determining a
temperature of the filter; and determining an amount of particulate
sediment in the filter, wherein the selection of one of the first
engine operation and the second engine operation is dependant on
the temperature of the filter and the amount of particulate
sediment in the filter.
16. The method of claim 13, calculating a first heat budget
including a first heat quantity from a first oxidation reaction of
burning accumulated particulates in the filter and a first quantity
of negative heat transfer between the filter and the exhaust
corresponding to the first engine operation; and calculating a
second heat budget including a second heat quantity from a second
oxidation reaction of burning accumulated particulates in the
filter and a second quantity of negative heat transfer between the
filter and the exhaust corresponding to the second engine
operation, wherein the selection of one of the first engine
operation and the second engine operation is dependant on the first
heat budget and the second heat budget.
17. The method of claim 16, further comprising: comparing the first
heat budget and the second heat budget; and selecting the operation
with the lowest corresponding heat budget.
18. The method of claim 16, further comprising calculating the
first heat quantity using a temperature of the filter, an amount of
particulate sediment in the filter, and an oxygen concentration in
the exhaust entering the filter as inputs.
19. The method of claim 16, further comprising calculating the
first quantity of negative heat transfer using a temperature of the
filter, an exhaust temperature entering the filter, and a flow rate
of the exhaust as inputs.
20. A system comprising: means for determining regeneration
conditions deviate from prescribed regeneration conditions during
regeneration of an exhaust particulate filter; and means for
selecting one of a first engine operation that increases heat
transfer from the filter to exhaust passing through the filter, and
a second engine operation that limits particulate combustion in the
filter.
Description
[0001] This application claims priority from Japanese Patent
Application Serial No. 2004-364479, filed Dec. 16, 2004, the entire
contents of which is incorporated herein by reference.
TECHNICAL FIELD
[0002] The invention relates to an internal combustion engine
having an exhaust particulate filter.
BACKGROUND
[0003] Some internal combustion systems include a particulate
capturing filter placed in the exhaust path. Such systems may
regenerate the particulate capturing filter by raising the filter
temperature under an engine operation that creates prescribed
regeneration conditions in a prescribed regeneration time to burn
the particulate sediment in the filter.
SUMMARY
[0004] Conditions in an exhaust particulate filter may deviate from
prescribed regeneration conditions when engine driving mode changes
from high-load drive to low-load drive during regeneration. Low
load drive reduces oxygen within the exhaust, which prevents
burning the particulates. However, depending on filter conditions,
by returning the engine to normal combustion, particulate sediments
captured in the filter may immediately burn out under excess oxygen
conditions, which can cause overheating of the filter. On the other
hand, if there are no particulate sediments, there is no danger of
overheating when the engine is returned to a lean combustion.
[0005] One aspect of the inventive method may reduce exhaust
particulate filter overheating potentially created if engine
operating conditions deviate from regeneration conditions during
the regeneration process. One of the two engine operations may be
selected: (1) a first engine operation with high heat release from
the filter, and (2) a second engine operation to limit particulate
oxidation to reduce heating from combustion of particulate
sediments in the filter. The operation selected cools the
particulate filter, and also depends on the filter conditions after
deviation from the prescribed regeneration conditions.
[0006] The regeneration conditions may also be adjusted depending
on filter conditions. In one instance the filter is controlled to
further reduce its temperature either by enhancing heat released
from the filter (the quantity of the negative heat transfer between
the filter and exhaust emission), or by reducing heat created by an
oxidation reaction of burning particulate accumulating in the
filter based on the temperature of the filter, and the amount of
particulate sediment in the filter.
[0007] In one embodiment, a system comprises a filter in an exhaust
path of an internal combustion engine that captures particulates
from exhaust in the exhaust path and a control unit that determines
when regeneration conditions deviate from prescribed regeneration
conditions during regeneration of the filter. Based on the
determination, the control unit selects one of a first engine
operation that increases heat transfer from the filter to the
exhaust, and a second engine operation that limits particulate
combustion in the filter.
[0008] In another embodiment, a method comprises determining
whether regeneration conditions deviate from prescribed
regeneration conditions during regeneration of an exhaust
particulate filter. The method further comprising selecting in
response to the determination, one of a first engine operation that
increases heat transfer from the filter to exhaust passing through
the filter and a second engine operation that limits particulate
combustion in the filter.
[0009] In another embodiment, a system comprises means for
determining regeneration conditions deviate from prescribed
regeneration conditions during regeneration of an exhaust
particulate filter. The system further comprises means for
selecting one of a first engine operation that increases heat
transfer from the filter to exhaust passing through the filter, and
a second engine operation that limits particulate combustion in the
filter.
[0010] The details of one or more embodiments of the invention are
set forth in the accompanying drawings and the description below.
Other features, objects, and advantages of the invention will be
apparent from the description and drawings, and from the
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0011] FIG. 1 is a schematic diagram illustrating an engine showing
one embodiment of the invention.
[0012] FIG. 2 is a flowchart for a main routine of diesel
particulate filter regeneration control.
[0013] FIG. 3 is a flowchart for a subroutine of discontinuance of
regeneration control.
[0014] FIG. 4 is a chart showing a combustion model of a divided,
retarded combustion.
DETAILED DESCRIPTION
[0015] FIG. 1 is a schematic diagram illustrating an engine 1,
e.g., a diesel engine, showing one embodiment of the invention. An
inlet compressor of a variable-nozzle supercharger 3, e.g., a
turbocharger, is provided in an intake air passage 2 of a diesel
engine 1. Intake air is supercharged by the inlet compressor and
cooled in an intercooler 4, and enters into a combustion chamber of
each cylinder after passing through an inlet air throttle 5 and a
collector 6. The intake air amount passing though the intake air
passage 2 is controlled by the open degree of the inlet air
throttle 5 provided in way of the intake air passage 2. [00161 Fuel
is forwarded to a common rail 8 under high pressure by a
high-pressure fuel pump 7 directly sprayed from a fuel injection
valve 9 of each cylinder into the combustion chamber. The air
entering the combustion chamber, and the fuel sprayed into the
combustion chamber are burned in the combustion chamber by
compression ignition and exhaust outflows through an exhaust path
10.
[0016] Part of the exhaust in the exhaust path 10 is refluxed to
the inlet side in an exhaust recirculation (hereinafter referred to
as "EGR") passage 11 via an EGR valve 12 as EGR gas by an EGR
system. The remaining exhaust passes through an exhaust turbine of
a variable-nozzle supercharger 3 to drive the turbine.
[0017] A diesel particulate filter (hereinafter referred to as
"DPF") 13 is provided downstream of the turbine in the exhaust path
10 to capture particulate exhausted in the exhaust.
[0018] Control unit 20 receives inputs from a variety of components
to control engine 1. For example, engine-speed sensor 21 detects
engine rotations Ne, accelerator position sensor 22 detects
accelerator position APO, air flow meter 23 detects the amount of
the intake air Qa, and water temperature sensor 24 detects the
engine coolant temperature Tw.
[0019] To detect pressure loss in the DPE 13, a differential
pressure sensor 25 detects the differential pressure .DELTA.P in
DPF 13, exhaust temperature sensors 26, 27 detect the exhaust
temperature Tin, Tout on both the inlet and outlet sides of the DPF
13, and an air/fuel ratio sensor (O2 sensor) 28 detects the
air/fuel ratio (oxygen concentration) of the exhaust emission
entering the DPF 13 are provided. Each of these signals are inputs
for the control unit 20.
[0020] Based on these input signals, the control unit 20 outputs: a
command signal for fuel injection into the fuel injection valve 9
to control the fuel injection amount and fuel injection timing with
the fuel injection valve 9, a command signal for opening into the
inlet air throttle 5, a command signal for opening into the EGR
valve 12, and a command signal for nozzle-opening into a
variable-nozzle mechanism 15 of the supercharger 3.
[0021] If the amount of particulate sediment captured in the DPF 13
increases, driving performance becomes worse due to increased
exhaust pressure. Control module 20 initiates regeneration based on
an estimated amount of particulate sediment in the DPF 13. Detailed
descriptions of the relevant DPF regeneration control are given
below.
[0022] FIG. 2 is a flowchart illustrating DPF regeneration control
by the control unit 20, and may be repeatedly exercised at a
predetermined time.
[0023] In step S1, controller 20 determines a value of the
regeneration flag, and if the value is 0 (nonregenerative), the
controller estimates the particulate sediment in the DPF 13 (C) in
step S2.
[0024] For example, controller 20 may detect the differential
pressure in the DPF 13 .DELTA.P by reading signals from the
differential pressure sensor 25. Controller 20 estimates flow rate
of exhaust emission SV by referring to a known function based on
the amount of the intake air Qa detected by the air flow meter 23,
and the reading of the injection quantity Qf to a fuel injection
valve 9. Controller 20 estimates particulate sediment in the DPF 13
based on the differential pressure .DELTA.P in the DPF and the flow
rate of exhaust emission SV. The more the differential pressure in
the DPF increases, the larger the estimated amount of particulate
sediment becomes because as the amount of particulate sediment
captured in the DPF 13 increases. However, the differential
pressure in the DPF varies according to the flow rate of exhaust
emission. If the amount of particulate sediment is the same, the
more the flow rate of exhaust emission increases, the more the
differential pressure in the DPF increases. Controller 20 corrects
the estimated amount of particulate sediment based on the flow rate
of exhaust emission.
[0025] In S3, controller 20 compares the amount of particulate
sediment estimated in S2 with the prescribed "particulate sediment
high" value (hereinafter referred to as "#PSH") to determine
whether or not the estimated amount of particulate sediment is
greater than or equal to #PSH.
[0026] In the case of the estimated amount of particulate sediment
<#PSH, controller 20 determines regeneration is not currently
required, thereafter S14 is followed to perform a normal control
(normal lean combustion in a diesel engine).
[0027] If the estimated amount of particulate sediment
.gtoreq.#PSH, controller 20 determines to regeneration is required,
thereafter S4 is followed.
[0028] In S4, controller 20 sets the regeneration flag to 1,
thereafter S5 is followed. If the regeneration flag is also
determined to be 1 (during regeneration) in S1, thereafter S5 is
followed.
[0029] In S5, it is determined whether or not the regeneration
conditions are established. Controller 20 determines whether or not
the operating conditions meet the regeneration conditions: if the
engine driving mode is in idle drive, slow-speed drive, and
ultra-low-speed drive (for example, less than 20 km/h), controller
20 determines that the regeneration conditions are not established,
thereafter S11 is followed. In other engine driving modes,
controller 20 determines that the regeneration conditions are
established; thereafter S6 and S7 are followed to regenerate the
DPF 13.
[0030] In S6, to complete regeneration of the DPF 13, controller 20
determines changes combustion from a normal lean combustion in a
diesel engine to a divided, retarded combustion. The divided,
retarded combustion includes a main or primary combustion to
generate engine torque and at least one preliminary combustion
prior to the main combustion. At least one of the preliminary
combustions requires fuel injection to occur on the compression
stroke. The main combustion requires fuel injection to start after
the preliminary combustion is completed.
[0031] In S7, the controller 20 sets the air/fuel ratio (the value
is represented as ".lamda.") to be comparatively rich (for example,
.lamda.=0.9 to 1.4) to control. When regenerating the DPF, the
exhaust .lamda. needs to be controlled from 0.9 to 1.4, and the
temperature of the DPF needs to be raised to over 600 degrees
Celsius. To control the exhaust .lamda. between 0.9 and 1.4, the
controller 20 controls the fuel injection amount and the air
throttle 5 to adjust the air amount taken in the combustion
chamber.
[0032] As shown in FIG. 4, controller 20 implements fuel injection
(a,b) for the divided, retarded combustion to promote a main
combustion to generate the main torque, and a preliminary
combustion prior to the main combustion by dividing the main
injection. The preliminary combustion occurs close to top dead
center (hereinafter referred to as "TDC"), and the main combustion
starts after the preliminary combustion is completed.
[0033] First, fuel is injected on the compression stroke (a), which
creates a preliminary combustion to raise the cylinder temperature
(temperature of the pressure connector) close to TDC. The injection
quantity to generate heat in the preliminary combustion depends on
the operating conditions. Thereafter, the fuel injected during
preliminary combustion maintains a cylinder temperature that
exceeds the temperature at which autoignition can happen during
fuel injection for the main combustion. The stability of the
preliminary combustion can be improved by changing the fuel
injection quantity and timing for the preliminary combustion
depending on the temperature of the pressure connector estimated
under each operating condition.
[0034] Subsequently, after the preliminary combustion is completed,
the fuel for the main combustion is injected after TDC.
[0035] While improving the controllability for the target
temperature with expanding the retard limitations by raising the
cylinder temperature with the preliminary combustion, controller 20
also controls smoke emission with the ignition delay time for the
main combustion, and raising the premix combustion ratio of the
main combustion by injecting the fuel for the main combustion after
the entire preliminary combustion is completed.
[0036] The interval between the commencing time of the preliminary
combustion and that of the main combustion depends on the engine
rotations. The interval may be at least 20.degree. crank angle (CA)
for the preliminary combustion (heat generation caused by the
preliminary combustion) to be completed. With such setup of the
interval, smoke deterioration can be prevented by preventing the
main combustion from deteriorating. The combustion speed is
extremely slow because the main combustion starts during the
expansion stroke, and the main combustion is completed after
50.degree. after TDC.
[0037] Delaying the termination time of the main combustion makes
the main combustion slower, which may prevent increased combustion
noise.
[0038] Such divided, retarded combustion can occur at high emission
temperatures and with low smoke under rich conditions, and
hydrocarbon emissions are low. The combustion under low .lamda.
conditions becomes stable, and high exhaust temperature can be
secured even if the injection timing of the main injection is
retarded because the retard limitations of the main combustion are
expanded by the preliminary combustion.
[0039] When the load on the engine is low, the high cylinder
temperature at the injection timing of the main injection requires
more than one time preliminary combustion because the combustion
timing of the main combustion to achieve the target exhaust
temperature greatly retards. In that case, controller 20 can
achieve low smoke and high exhaust temperature with a plurality of
preliminary combustions even under low load conditions.
[0040] During regeneration of the DPF 13 in S6,S7, particulate
sediment in the DPF 13 (C) is estimated in S8 just as S2.
[0041] In S9, controller 20 compares the amount of particulate
sediment estimated in S8 with the prescribed "particulate sediment
low" value (hereinafter referred to as "#PSL") to determine the
completion of regeneration to determine whether or not the
estimated amount of particulate sediment .ltoreq.#PSL.
[0042] In the case of the estimated amount of particulate sediment
>#PSL, controller 20 determines regeneration is not complete,
and regeneration continues.
[0043] In the case of the estimated amount of particulate sediment
.ltoreq.#PSL, controller 20 implements regeneration, thereafter S10
is followed to return by resetting the regeneration flag to 0.
[0044] On the other hand, if the exhaust particulate filter
deviates from the regeneration conditions during regeneration, to
be more precise, if the engine driving mode changes to idle drive,
S11 is followed by S5 to stop regeneration.
[0045] Temperature Tdpf of the DPF 13 is estimated in S11. Exhaust
temperature Tin on the inlet side, and exhaust temperature Tout on
the outlet side of the DPF are detected by signals from the exhaust
temperature sensors 26,27 for DPF temperature Tdpf to be estimated.
To be more precise, it is estimated using the following equation,
with 0<k<1: Tdpf=k*Tin+(1-k)*Tout (Equation 1).
[0046] In S12, controller 20 determines whether or not DPF
temperature Tdpf is lower than the prescribed temperature #TMP.
This occurs where the temperature of the DPF 13 is lowered enough
when regeneration of the DPF 13 has not been commenced, or by
discontinuance of regeneration control.
[0047] In the case of DPF temperature Tdpf.ltoreq.#TMP, there are
no problem with changing to normal lean combustion in the diesel
engine, therefore S14 is followed to change to normal control
(normal lean combustion in the diesel engine). At this time, the
regeneration flag is reset to 0 in S15.
[0048] In the case of DPF temperature Tdpf>#TMP, thereafter S13
is followed to execute the discontinuance of regeneration control
(sub routine in FIG. 3).
[0049] FIG. 3 is a flowchart for a sub routine of the
discontinuance of regeneration control to be executed in S13 of the
flow in FIG. 2. In this flow, one of two engine operations is
selected depending on the conditions of the DPF 13.
[0050] The first engine operation is an operation with higher heat
released from the DPF 13 (quantity of the negative heat transfer
between the DPF 13 and exhaust emission) than the second engine
operation, in other words, the exhaust temperature entering the
filter is so low that there is a high oxygen surplus, to put it
simply, it is a lean operation. Of the first engine operation (lean
operation), the DPF 13 is cooled by the exhaust emission so that
the heat released from the DPF 13 will be higher because the
temperature of the exhaust emission is low. However, the heating
value in the DPF 13 (heat quantity by an oxidation reaction arising
from burning particulate accumulating in the DPF 13) may be higher
than the heat released because of an oxygen surplus depending on
the conditions of the DPF 13.
[0051] The second engine operation is an operation with lower
heating value in the DPF 13 (heat quantity by an oxidation reaction
arising from burning particulate accumulating in the DPF 13) than
the first engine operation, in other words, the exhaust temperature
entering the filter is so high that there is a low oxygen surplus,
to put it simply, it is a rich operation. Of the second engine
operation (rich operation), the heating value in the DPF 13 becomes
low because there is a low oxygen surplus. However, the heat
released from the DPF 13 (quantity of the negative heat transfer
between the DPF 13 and exhaust emission) may be lower than the
heating value depending on the conditions of the DPF 13 because the
exhaust temperature is high.
[0052] In comparison with the divided, retarded combustion under
low ) conditions used for regeneration, the first and second engine
operations have normal injection timing (close to TDC) in the
diesel engine without dividing the main injection, and retarding
the injection timing. As discussed with respect to FIG. 2, normal
operation of the engine 1 uses a lean air/fuel ratio, while
regeneration of the DPF 13 requires a much richer air/fuel ratio.
The first and second engine operations require air/fuel ratios
within the range of an air/fuel ratio for normal operation and an
air/fuel for regeneration of the DPF 13. Specifically, the first
engine operation uses an air/fuel ratio as rich or richer than the
normal lean combustion in the diesel engine, but leaner than the
divided, retarded combustion during regeneration. The second engine
operation also uses an air/fuel ratio as lean as, or leaner than
the divided, retarded combustion during regeneration, but richer
than the first engine operation and normal lean combustion.
[0053] Temperature Tdpf of the DPF 13 is estimated in S101 just as
S11. Particulate sediment C in the DPF 13 is also estimated just as
S2,S8. The flow rate of exhaust emission SV is estimated by the
amount of the intake air Qa detected by the air flow meter 23, and
the reading of the injection quantity Qf to a fuel injection valve
9.
[0054] In S102, forecasting calculations of the oxidation reaction
speed (combustion speed) SPD1,SPD2 arising from burning particulate
accumulating in the DPF 13 are performed of the first engine
operation (lean operation), or the second engine operation (rich
operation).
[0055] The oxidation reaction speed SPD is estimated using the
following equation, with k the reaction rate constant, Ea the
activation energy constant, R the gas constant, Tdpf the DPF
temperature, C the amount of particulate sediment and O the oxygen
concentration of the exhaust emission entering the DPF:
SPD=k*e.sup.(-Ea/R/Tdpf)*C*O (Equation 2) In equation 2, k is the
reaction rate constant, Ea is the activation energy constant, R is
the gas constant, Tdpf is the DPF temperature, C is the amount of
PM sediment, and O is the oxygen concentration of the exhaust
emission entering the PDF.
[0056] The oxidation reaction speed SPD can be estimated using the
following equation as functions of DPF temperature Tdpf, amount of
particulate sediment C, and oxygen concentration O because K, Ea,
and R are constant. SPD=f(Tdpf, C, O) (Equation 3)
[0057] The oxidation reaction speed SPD1=f (Tdpf, C, O1) of the
first engine operation is estimated assigning the current DPF
temperature Tdpf, the current amount of particulate sediment, and
the oxygen concentration (predicted value) O=O1 of the first engine
operation to the above Equation 3.
[0058] The oxidation reaction speed SPD2=f (Tdpf, C, O2) of the
second engine operation is estimated assigning the current DPF
temperature Tdpf, the current amount of particulate sediment, and
the oxygen concentration (predicted value) O=O2 of the second
engine operation to the above Equation 3.
[0059] In S103, forecasting calculations of the velocity of the
negative heat transfer between the DPF 13 and exhaust emission
q1,q2 are performed of the first engine operation (lean operation),
or the second engine operation (rich operation).
[0060] The velocity of the negative heat transfer between the DPF
13 and exhaust emission is estimated using the following equation,
with a the heat transfer coefficient, Tdpf the DPF temperature,
Tgas the temperature of the exhaust emission entering the DPF, SV
the flow rate of exhaust emission, and A the effective superficial
area of DPF: q=.alpha.*(Tdpf-Tgas)*SV*A (Equation 4)
[0061] The velocity of the heat transfer q can be estimated using
the following equation as functions of DPF temperature Tdpf,
temperature of the exhaust emission, and flow rate of exhaust
emission SV because .alpha. and A are constant: q=f(Tdpf, Tgas, SV)
(Equation 5)
[0062] Therefore, the velocity of the heat transfer q1=f (Tdpf,
Tgas 1, SV) of the first engine operation is estimated with the
current DPF temperature Tdpf, the current temperature of the
exhaust emission (predicted value) T gas=T gas 1 in the case of the
first engine operation, and the current flow rate of exhaust
emission SV in the above Equation 5.
[0063] Also, the quantity of the heat transfer q2=f (Tdpf, Tgas 2,
SV) of the second engine operation is estimated with the current
DPF temperature Tdpf, the current temperature of the exhaust
emission (predicted value) T gas=T gas 2 in the case of the second
engine operation, and the current flow rate of exhaust emission SV
in the above Equation 5.
[0064] Integration of the oxidation reaction speed SPD1, SPD2 in
the case of the first and second engine operations estimated in
S102, heat quantities by oxidation reactions (heating values)
QGEN1, QGEN2 in the case of the first and second engine operations
are estimated in S104: QGEN1=.SIGMA.(SPD1) (Equation 6)
QGEN2=.SIGMA.(SPD2) (Equation 7)
[0065] Integration of the velocity of the negative heat transfer
between the DPF 13 and exhaust emission q1,q2 in the case of the
first and second engine operations estimated in S103, quantities of
the negative heat transfer (heat released) QRAD1, QRAD2 in the case
of the first and second engine operations are estimated in S105:
QRAD1=.SIGMA.(q1) (Equation 8) QRAD2=.SIGMA.(q2) (Equation 9)
[0066] In S106, a heat budget of the first engine operation (the
difference between the heating value QGEN1 and the heat released
QRAD1, equal to QGEN1-QRAD1, is estimated; and a heat budget in the
case of the second engine operation, equal to QGEN2-QRAD2 is
estimated. These heat budgets will show the trend of rising
temperature in the case of each operation. If the heat budget is
positive, the temperature of the DPF 13 will rise; and if it is
negative, the temperature of the DPF 13 will fall.
[0067] It is determined whether or not QGEN1-QRAD1<QGEN2-QRAD2
in S106: if YES, the heat budget of the first engine operation
means the temperature of the DPF 13 will fall, thereafter, S107 is
followed to select the first engine operation (lean operation).
[0068] If NO is the determination in S106, it will be
QGEN1-QRAD1>QGEN2-QRAD2, the heat budget of the second engine
operation means the temperature of the DPF 13 will fall,
thereafter, S108 is followed to select the second engine operation
(rich operation).
[0069] As described above, according to the embodiments, if the DPF
13 deviates from the regeneration conditions during regeneration,
the DPF 13 can be controlled toward the direction where the
temperature of the DPF 13 will further fall so that overheating of
the filter can be avoided, by selecting either one of the two
engine operations between the first engine operation with higher
heat released from the DPF 13 (quantity of the negative heat
transfer between the DPF 13 and exhaust emission), and the second
engine operation is an operation with lower heating value in the
DPF 13 (heat quantity by an oxidation reaction arising from burning
particulate accumulating in the DPF 13) depending on the conditions
of the DPF 13.
[0070] The first engine operation uses a lower exhaust temperature
entering the DPF 13 and a high oxygen surplus (lean operation); and
the second engine operation is an operation with higher exhaust
temperature entering the DPF 13 and a low oxygen surplus (rich
operation). Both operations can be carried out by control unit 20
by controlling the fuel injection amount and fuel injection timing,
opening into the inlet air throttle 5, opening the EGR valve 12,
and nozzle-opening into a variable-nozzle mechanism 15 of the
supercharger 3.
[0071] The conditions of the DPF 13 can be determined with
precision by determining based on the temperature of the DPF 13 and
particulate sediment in the DPF 13. The conditions of the DPF 13
can be determined with precision by calculating the heat quantity
by an oxidation reaction arising from burning particulate
accumulating in the DPF 13, and the quantity of the negative heat
transfer between the DPF 13 and exhaust emission in the case of the
first and the second engine operations respectively based on the
temperature of the DPF 13 and particulate sediment in the DPF
13.
[0072] These calculations produce the heat budgets of the first and
second engine operations. The temperature of the DPF 13 can be
lowered by comparing the heat budget of the first engine operation,
and the heat budget of the second engine operation, and by
selecting the operation with the lowest heat budget.
[0073] The heat quantity by an oxidation reaction arising from
burning particulate accumulating in the DPF 13 can be predicted
with precision by predicting the temperature of the DPF 13 (Tdpf),
particulate sediment in the DPF 13 (C), and the oxygen
concentration of the exhaust emission entering the DPF (O).
[0074] The quantity of the negative heat transfer between the DPF
13 and exhaust emission can be predicted with precision by
predicting the temperature of the DPF 13 (Tdpf), temperature of the
exhaust emission entering the DPF (Tgas), and the flow rate of the
exhaust emission entering the DPF 13 (SV).
[0075] The temperature of the DPF 13 (Tdpf) can be predicted with
precision by measuring the exhaust temperature detected by the
exhaust temperature sensors 26,27 provided on both the filter inlet
and the filter outlet sides.
[0076] The particulate sediment in the DPF 13 (C) can be predicted
with precision by measuring the differential pressure in the DPF 13
.DELTA.P, and the flow rate of the exhaust emission entering the
DPF 13 (SV).
[0077] The oxygen concentration of the exhaust emission entering
the DPF (O) can be easily reduced to practice by determining based
on type of operations, the first and the second respectively.
[0078] The temperature of the exhaust emission entering the DPF
(Tgas) can be easily determined by determining based on type of
operations, the first and the second respectively.
[0079] The flow rate of the exhaust emission entering the DPF 13
(SV) can be predicted by predicting the detected value of an air
flow meter 21 provided in an engine inlet system, and the reading
of the injection quantity Qf to a fuel injection valve 9.
[0080] Various embodiments of the invention have been described.
These and other embodiments are within the scope of the following
claims.
* * * * *